2005 AMC 10A Problems/Problem 9
Contents
[hide]Problem
Three tiles are marked and two other tiles are marked . The five tiles are randomly arranged in a row. What is the probability that the arrangement reads ?
Solution1
There are distinct arrangements of three 's and two 's.
There is only distinct arrangement that reads .
Therefore the desired probability is
Solution2
Imagine you need to fit the two Os into the gaps between the three Xs.
The gaps between the Xs are: _X_X_X_, a total of 4.
You need to fit two Os in the gaps. There are two possible outcomes:
1. The two Os are put into different gaps, in this case the number of arrangements is 4 x 3 / 2 = 6
2. The two Os are put into the same gap, in this case there will be an extra 4.
Therefore the probability of arrangements that reads XOXOX is 1 / (4 + 6) = 1 / 10
~Dew grass meadow
See also
2005 AMC 10A (Problems • Answer Key • Resources) | ||
Preceded by Problem 8 |
Followed by Problem 10 | |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 | ||
All AMC 10 Problems and Solutions |
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